The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hybrid vehicles (HEVs) have propulsion systems that consist of at least one electric motor or electric machine in combination with at least one other power source. Typically, the other power source is a gasoline or diesel engine. There are various types of HEVs depending on how the electric motor(s) and other power source(s) are combined with one another in order to provide propulsion for the vehicle, including series, parallel and compound HEVs.
Powertrain architectures for HEVs manage the input and output torques of various prime movers, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to an energy storage system, comprising a battery pack. The internal combustion engine in a series HEV is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel HEV architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for wide range operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel HEV powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions (i.e., input-split, output-split and compound-split configurations) thereby enabling high-torque continuously variable speed ratios, electrical energy-dominated launches, regenerative braking, engine off idling, and two-mode operation.
As noted, such complex EVT HEVs utilize one or more electric machines and require advanced energy transmission, conversion and storage systems to supply electrical energy to and receive and store electrical energy from these machines, and typically comprise, for example, at least one electric machine, power inverter module, power bus, electrical energy storage device (ESD), such as a battery, as well as various control electronics, control algorithms and other associated items. The ESD may comprise any suitable energy storage system that is adapted for high-density energy storage, including a battery, ultracapacitor, or other high-density energy storage device. As used herein, reference to a battery includes not only a single battery, also includes any combination of single or multiple batteries, or cells thereof, into a battery pack or array, or a plurality of battery packs or arrays. As used herein, the term battery generally refers to any secondary or rechargeable battery.
Current system operation is described with reference to an operator torque request, To_req, in the form of an accelerator pedal tip-in/tip-out maneuver. The operator torque request (To_req) is typically input to the system via the accelerator pedal, to generate an output torque command (To_cmd) in the hybrid control system. The hybrid control system monitors system operation at each operating point as the vehicle accelerates, and determines power flow from the electrical machine and the engine through the EVT for each point, typically using engine speed and torque as two key criteria to determine the power flow from the primary power source and the hybrid transmission system. Determining these points along with the operator torque request solves the dynamic system equations and determines the power flow from the energy storage system. The engine generates a torque input, with additional torque generated by electrical energy which is transferred to the electric machines to generate torque that is transmitted to the EVT.
In operation, the overall control scheme determines the operator torque request, To_req, and determines an optimum torque input, Opt_Ti, from the engine to meet the torque request. The optimum torque input preferably comprises an input torque determined within a solution space of feasible input torques in accordance with a plurality of powertrain system constraints that results in a minimum overall powertrain system loss. A preferred method for determining the optimum torque input is described in detail in commonly assigned U.S. Pat. No. 7,076,356 B2, which is incorporated by reference in its entirety. From the optimum input torque, motor torques output from the electrical motor(s) is determined, and electrical energy transfer to the electrical motor(s) is adjusted to operate the powertrain system to meet the operator torque request.
Output from the engine typically includes torque transferred to the input of the transmission, and accessory loads. The accessory loads are often driven by separate pulleys output from the engine, and include such devices as air-conditioning compressors and pumps. Furthermore, passenger compartments for vehicle systems consume electrical power originating from the electrical storage devices. Power consumed by the accessory loads is normally estimated by the control system and not directly measured; therefore some loads are often unaccounted for in determining the optimum torque input from the engine. In addition conditions may exist at which the engine is unable to produce the desired torque due to extreme high or low ambient and operating temperatures, variations in fuel quality, component wear and deterioration, and system or component faults. Under such operation, the engine may not produce the optimum input torque to the transmission when the engine speed and torque are commanded to the speed/load operating point, i.e., Ne and Te. Torque output from the electrical motor(s) is controlled to meet the operator torque request, consuming additional electrical power.
Therefore, there is a need for a control scheme which control operation of the powertrain system to minimize unexpected, unanticipated, or unaccounted for electrical power during ongoing operation.